The invention relates to reinforced shaped composites and laminates. More specifically, the invention relates to a process for manufacturing shaped composites and laminates reinforced with long or continuous fibers and/or filaments or chopped-aligned fibers or filaments, such as carbon matrix composites (FRCC's), ceramic matrix composites (FRCMC's), glass matrix composites (FRGMC's), glass-ceramic matrix composites (FRGCMC's), metal matrix composites (FRMMC's), intermetallic matrix composites (FRIMC's), cement, concrete or gypsum matrix composites and reinforced plastic composites and to filament tapes, ribbons, sheets or cloths for use in said process.
Composites and laminates, i.e. combinations of two or more materials, comprising matrix material(s) and reinforcing fillers, which form a bonded quasi-homogeneous structure with synergistic mechanical and physical properties compared to the basic matrix and filler materials, form an important class of construction materials in modern technology. Composites may be of two different types, viz. composites comprising a matrix with discontinuous filler system particles, platelets, whiskers, i.e. short fibers, flakes and chopped fibers, i.e. fibers of a length between say 3 mm and about 20 cm and composites comprising a matrix with preform moulding of long or continuous fibers and/or filaments. Laminates generally comprise a matrix with a number of laid up webs of long or continuous fibers and/or filaments or chopped fibers or filaments.
In principle the composites with chopped and in particular with continuous fibers and/or filaments and the laminates form preferable construction materials because they combine desirable intrinsic physical and/or chemical properties of the matrix with favourable strength and stiffness properties derived from the fibers and/or filaments. The chopped fibers or filaments and the long continuous fibers or filaments are basically used in four configurations (vide Kirk Othmer, Encyclopedia of Chemical Technology, third Edition, Supplement Volume, page 261) of which the unidirectional configuration (long or continuous fibers or filaments arranged substantially parallel to each other) and chopped-aligned configuration (chopped fibers or filaments all arranged in the same direction) in principal give the best performance. Because fibers afford significant control over the internal structure of the composite and because of their high aspect ratios (ratio of length to diameter), long, continuous fibers are the reinforcing elements of choice in high performance composites.
However, according to Mittnick and Mc. Elman in a paper entitled "Continuous Silicon Carbide Reinforced Metal Matrix Composites" presented at the SME Metal Matrix Composites '88 Conference, September 1988, pages 91-99, it is difficult when manufacturing composites which generally involve complex geometric shapes, to position continuous fibers during the fabrication process. The system described by Mittnick and Mc. Elman, the so called "green tape" system, the "plasma-sprayed aluminium tape" system and the "woven fabric" system of which the latter is said to be perhaps the most interesting, are indeed only suitable for manufacturing laminates of rather simple shape. In all these systems separate fiber sheets, each comprising a single layer of straight and parallel fibers held together by a temporary or permanent binder or cross-wave, are sequentially laid up into a mould in the required orientation to fabricate laminates. The method described for making the green tape comprises winding the fibers or filaments onto a foil-covered rotating drum, overspraying the fibers with a (temporary) resin binder, followed by cutting the layer from the drum to provide a flat sheet which is used for making a preform moulding by laying up. This method requires a careful control of the winding operation to keep the fibers or filaments parallel with the correct spacing. But even then, when the sheet or laid up and subsequently the temporary resin binder is removed, the orientation of the filaments gets at least partly lost.
In European patent application EP 249927 it is suggested to apply bundles of continuous fibers or filaments having fine particles, short fibers and/or whiskers deposited on the individual surfaces of the continuous fibers of filaments as reinforcing system for composites and/or laminates. These bundles of continuous fibers or filaments with fine particles, short fibers and/or whiskers deposited on the individual surfaces of the continuous fibers or filaments are formed by introducing said particles, short fibers and/or whiskers into a bundle of loose fibers or filaments. Under these circumstances a more or less uniform and homogeneous result is only obtained when both fine particles and short fibers or whiskers have been deposited on the individual surfaces of the continuous fibers or filaments. When only fine particles have been deposited on the surfaces of the continuous fibers, the fibers tend to bunch and when only whiskers or short fibers have been deposited on the surfaces of the continuous fibers or filaments, it is difficult to prevent the fibers or filaments from contacting each other. Filaments are easily damaged by the (sharp) materials deposited on the surfaces of the other filaments, and deposited material easily falls out and potentially damages shaping equipment.
A general problem encountered by applying usual preforms, produced from fiber products, is that the matrix cannot infiltrate sufficiently and homogeneously in between the bundles and the monofilaments of the reinforcement fibers. The interstitial space within the fiber bundles is often much smaller than the spaces between the fiber bundles used to produce the preform, and the rate of bundles infiltration relative to the preform infiltration become insufficient.
An object of the invention now is to provide composites and laminates reinforced with long or continuous fibers and/or filaments in a unidirectional configuration or with long chopped fibers or filaments in a chopped-aligned configuration. More in particular an object of the invention is to provide a process for manufacturing such composites or laminates in a cheap, easy and reliable manner, without the problems mentioned herein before. A further object is, to enable the application of automated and/or controlled thermoplastic type fabrication/melt-shaping techniques to shape complex preforms. A further object is, to avoid damage and/or degradation to the fibers/monofilaments during shaping and/or processing. A further object is, to avoid clustered fibers in the shaped preform. A further object is to substantially avoid preform shrinkage. A further object is to "tailor" the permeability of the preform. A further object is to ease the forming of a tailored matrix mix. A further object is to reduce the number of production steps, and/or production time and/or firing cycles. A further object is to obtain net-shape or near net-shape composite articles and/or integrated systems substantially eliminating costly machining. A further object is, to provide a novel green tape, ribbon, sheet or cloth with long or continuous fibers and/or filaments, which is suitable for use in the process of manufacturing composites or laminates according to the invention and which can produce a dense composite material. Further objects and advantages of the invention will appear from the following description of the principles and preferred embodiment of the invention.
It has been found that a correct, stable orientation of long or continuous reinforcing fibers or filaments is easily obtained when a number of long or continuous reinforcing fibers or filaments, say tow, roving or yarn, of such fibers or filaments is spread out in a single layer or a limited number of multi-layers, fibers or filaments are spaced by particles, such as granules, platelets, whiskers or flakes which are uniformly distributed between the fibers or filaments and this arrangement is fixed by means of flexible, organic- or other binder, thus forming a green tape, ribbon, sheet or cloth and that such a tape, ribbon, sheet or cloth can be arranged (e.g. by braiding, compressing, laminating, pultrusion, rolling, winding or weaving) to form a preform moulding wherein the fiber/monofilaments are protected during handling/shaping and the orientation and spacing of the fibers or filaments are maintained, thanks to the binders. These preform mouldings then are used as a reinforcing structure in manufacturing advanced composites and laminates, in particular carbon, ceramic, glass, glass-ceramic, metal and intermetallic composites. The invention is based on these findings.